Many mechanical operations require that one or more workpieces be held stationary for a period of time. Various types of clamps and other devices are known in the art for securing a workpiece in a desired position to facilitate an operation on the workpiece.
An apparatus for securing one workpiece at a time is disclosed in U.S. Pat. No. 4,805,888 to Bishop. The Bishop patent describes a two-piece adjustable clamp where the bolt-like portion of each clamp has a lower end threaded into a cooperating tapped hole of a platen, and has an eccentrically-offset upper end about which a shallow nut-like portion is socketed for orbital camming movements. However, Bishop has vertical walls where only one of the vertical walls can hold a workpiece laterally when the bolt-like portion is fastened to the platen.
Another apparatus for securely holding a workpiece is described in U.S. Pat. No. 5,310,299 to Bernstein. The Bernstein patent describes a clamping member having a concentric conical bore for receiving a fastener therethrough which when turned engages against the inner bearing surface of the conical bore providing a single lateral force which urges the clamping member toward a workpiece and a stop. Thus, the clamping device of Bernstein's has only a single vertical surface which can hold a workpiece securely against a stop.
Accordingly, both clamping devices described by Bishop and Bernstein solely produce a single lateral or horizontal force for securing a workpiece against a stop on a platen which is inadequate for securing a workpiece during machining and only one side of both their devices can hold a workpiece. Consequently, these clamps and other known clamping devices have failed to secure workpieces when a cutting machine is removed from the workpiece. That is, when a cutting machine such as a drill or slitting saw is inserted into the workpiece there is usually no problem as the horizontal or lateral force holds the workpiece; but, when the drill or slitting saw is removed, the workpiece pops or jumps out of the clamp.
Furthermore, in addition to the downtime caused by the workpiece or several workpieces jumping out of the clamp, the jolt which causes the workpieces to pop out also causes damage to the clamp. Thus, considerable time and money are lost in replacing the workpieces and the clamps due to this prior design.
The above problem was solved with the gripping device which is disclosed in U.S. patent application Ser. No. 08/555,869, filed Nov. 13, 1995. That application is incorporated herein by reference.
U.S. Pat. No. 3,473,420 to Boggs shows an apparatus for positioning and clamping one or more workpieces. However, three points of contact are required to hold each workpiece and thus, at least two positioning blocks are needed to secure a single workpiece. As a result, a large portion of the platen or jig is devoted to positioning blocks or stops and not to the workpieces. Consequently, a longer time is required to secure each block, and, additional expense is incurred in the use of the larger or more platens that are needed to secure the workpieces.
Applicant is aware of a two-piece clamping device which is produced under the name KIRK VISE. However, that clamp employs rubber parts and has a conical through bore surface which limits what one can clamp down and has too much travel. Moreover, this clamping device breaks down after limited amount of use causing downtime and additional expense in replacing the worn clamping devices.